Bad-tasting mineral water

If bottled mineral water is left out in the sun, it often develops an unpleasant taste. Until recently, nobody quite knew why. Now there is evidence of what actually causes the bad flavor and what can be done to prevent it.

In 2007, Germans drank an average of 172.4 liters of mineral water each. Consumers expect the drink to be both refreshing and thirst-quenching, without any noticeable taste of its own. The bottled-water industry uses automatic sniffer devices at the filling plants to separate out any odd-smelling return bottles. But tasting tests carried out by German consumer safety group Stiftung Warentest have shown that unpleasant flavors can nevertheless keep occurring in the water. Investigations by the Fraunhofer Institute for Process Engineering and Packaging IVV in Freising have confirmed this: 43 percent of the tested samples exhibited a "plastic-like" smell referred to by experts as a "sunlight odor". Five percent were found to taste musty or moldy, and 14 percent had a fruity note to them.

Andrea Strube of the IVV has now identified the substances responsible for the sunlight odor and flavor. "Its development is accelerated by direct sunlight," says the chemist. "Everyone has experienced this: If you leave a plastic bottle out in the sun for a long time, the drink tastes unpleasantly of plastic afterwards." Until now, most people assumed this was due to the lubricant applied to bottle caps to enable users to open them without undue effort. Strube analyzed the odor by breaking down the volatile substances into their individual components, which were then subjected to a smell test performed by humans. This showed that the unwanted constituents can be attributed to not just one but several chemical compounds, so the plastic smell does not come from the lubricant alone. Strube suspects it is triggered by impurities in the lubricant or other packaging additives.

Musty components aren't easy to avoid either. These usually form after consumers have kept fruit juices or other drinks in the PET return bottles. If residues are left behind in the bottles, these can become moldy, producing odorous substances that seep into the wall of the bottle and are later released into the mineral water. The sniffer devices at the filling plants aren't able to recognize these bottles, as the concentration of odors in the air is much too low. Only the human senses can detect them. Strube was able to identify the responsible substances and is now in search of the microorganisms that produce them. "We hope this will help us to find a way of automatically detecting foul-smelling bottles."

Source: Fraunhofer-Gesellschaft